The present invention relates in general to propulsion apparatus for aircraft and, in particular, to a new and useful combination, including a rotary engine having a power output shaft, the rotary engine being positioned near the center of gravity of the aircraft, with the output shaft extending at an angle to the longitudinal axis of the aircraft, and a pusher propeller mounted for rotation near the rear of the aircraft and connected to the output shaft for rotation of the propeller.
In a known propulsion or power drive train, as described in the publication "Aero", May 1971, pages 108-110, the longitudinal axis of an engine power output shaft is arranged essentially parallel to the aircraft longitudinal axis. The engine power take-off shaft is coupled with an extension shaft which extends up to the tail of the fuselage and also in the direction of the aircraft longitudinal axis. The tail end of the horizontal shaft is connected to a vertical shaft by means of a miter gear, which vertical shaft extends up to the upper region of the empennage. The upper end of the vertical shaft is connected to a propeller shaft extending essentially parallel to the aircraft longitudinal axis, the connection also being by means of a miter gear. Viewed in the flight direction, the propeller is arranged in front of the empennage.
Such a propulsion arrangement makes it possible for the aircraft to take off and land at a large angle of attack without running the danger of the propeller touching the ground, even with the comparatively short landing gear. The short take-off and landing properties connected therewith permit even relatively inexperienced pilots to use airfields with short runaways. This propulsion arrangement has, however, the disadvantage of long complication drive trains between engine and propeller. Such a drive train is not only burdened with considerable weight problems, but also difficulties arise, particularly with the vibration-free integration of bearings for the shafts, as well as the redirection gear boxes. The drive train is also prone to the malfunction, because of the multiplicity of parts. An additional disadvantage is the fact that transmissions which change the direction of propulsive power through about 90.degree., have relatively high maintenance costs. In this connection, one has to additionally consider the heat generation in the region of the miter gear boxes which requires additional cooling arrangements. The diameter of the propeller is also limited by the clearance which is needed to the upper surface of the fuselage.
A construction type of this species is disclosed in German patent No. 7 22 883. A considerable disadvantage of this type of construction is due to the fact that the propeller shaft extends coaxially with the inclined extension shaft, and is arranged at a relatively large angle of inclination with respect to the aircraft longitudinal axis. Such a propeller arrangement may indeed have advantages during the take-off phase for an aircraft. During flight, however, especially during cruising flight, which is performed essentially in a horizontal attitude, the incident flow conditions in front of the pusher propeller are very inexact and aerodynamically, extraordinarily unfavorable.
The fact that the engine is located very far behind the center of gravity of the aircraft is also a disadvantage. Such a layout for an engine in an aircraft, is, in certain circumstances, sensible in the known types of construction with an inclined propeller shaft. It requires, however, the arrangement of balancing weights in the nose section of the aircraft which, while compensating for the tail heaviness of the aircraft, considerably increases its overally weight.
Another disadvantage of the known type of construction consists in circumstances that, because of the comparatively low location of the propeller shaft, a portion of the pusher propeller lies in the interference field of the empennage, as well as in the wake flow of the fuselage.
A relocation of the propeller shaft into an essentially undisturbed region above the longitudinal axis of the aircraft is hardly possible in the known designs, since such a measure would involve an even larger inclination of the propeller shaft, with all the disadvantages connected therewith. This means that the diameter of the pusher propeller is also relatively small. The propeller rpm must, therefore, be high. This lowers the propeller efficiency. The take-off power deteriorates, and fuel consumption is high with a comparatively large generation of noise.